240 LITTORINID^. 



fold, but differs in its fusiform outline, narrow aperture, and 

 distinct canal. In its general appearance resembles Paseio- 

 laria, but has only one instead of two or three columella-folds, 

 and is destitute of ornamentation, and its outer lip is smooth 

 within. 



Cryptoplocus, Pictet and Campiche, 1854. 



Etym. — Cryptos, hidden, ploce, a plait. 



Distr. — t sp. Jurassic and Cretaceous ; Prance, Switzerland, 

 Germany. G. monilifera, d'Orb. 



Shell as in Nerinsea, without columella and labial plaits ; one 

 plait on the posterior face of the aperture, a disposition very 

 analogous to that in some Cerithiums, such as C. nodulosum ; 

 aperture rounded, not channeled in front ; umbilicated or im- 

 perforate. 



Aptyxis, Zittel, 18t3. 



Syn.' — Pachyst3'lus, Gemmellaro, 1818. 



Distr. — A. nexcostata^ d'Orb. Jurassic. 



Shell turreted, nearly cylindrical, not umbilicated ; mouth 

 lengthened quadrangular ; inner and outer lips without folds ; 

 columella with a median fold-like thickening. 



Pamily LITTORINIDJE. 



Shell spiral, turbinate or globular ; peritreme entire, interior 

 not nacreous. 



Operculum corneous, spiral or paueispiral. 



Animal having a proboscidiform head with terminal mouth, 

 and conical tentacles, subulate, with eyes at their outer bases. 



The species inhabit the sea, brackish or fresh water, some being 

 amphibious. The}^ are mostly littoral, feeding on algae. Den- 

 tition (xi, 26). 



LiTTORiNA, Perussac. 



Etym. — Littoralis, belonging to the sea-shore. Periwinkle. 



Syn. — Bacalia, Gray. Isonema, Hall (in part). 



Distr. — 175 sp. L. littorea, Linn. (Ixix, 1 9). The periwinkles 

 are found on the sea-shore in all parts of the world. In the 

 Baltic they live within the influence of fresh water, and fre- 

 quently become distorted in consequence ; similar monstrosities 

 are found fossil in the Norwich crag of England. 



Possil. Eather numerous ; Miocene — . Probably some of 

 the older fossils referred to Turbo, etc., belong to this genus. 



Shell turbinated, thick, pointed, few-whorled ; aperture rounded, 

 outer lip acute, columella rather flattened, imperforate. Oper- 

 culum paueispiral, lingual teeth hooked and trilobed ; uncini 

 hooked and dentated. 



